1. Field of the Invention
The present invention relates to a semiconductor device including field-effect transistors having a gate insulation film and a manufacturing method thereof, and more particularly, to the semiconductor device and the manufacturing method thereof suitable for further shrinking the transistor size.
2. Description of the Related Art
As the structure used for a semiconductor device in which field-effect transistors having a gate insulation film are integrated which structure is to electrically isolate regions in which these transistors are disposed (element isolation), there is a structure disclosed in, for example, Japanese Patent Laid-open Application No. Hei 9-181166. This Japanese Patent Laid-open Application No. Hei 9-181166 describes the structure in which element isolation is achieved by forming trenches in a substrate and burying an oxide in the trenches, instead of by selective oxidation.
The structure using an insulator buried in the trenches as the element isolation structure is becoming a mainstream structure as the scaling down of elements progresses. Methods of forming the trenches and the order of the trench forming processes vary depending on the kinds or the like of elements to be formed.
Among such semiconductor devices, a semiconductor device in which trenches for element isolation regions are formed in a substrate to pass through a gate insulation film after the gate insulation film and so on are formed on the substrate has an advantage that the processes can be simplified and, for example, the structure for avoiding the concentration of electric field on an end part of the gate insulation film can be easily achieved. Here, anisotropic etching, for example, an RIE (reactive ion etching) method is adoptable for forming the trenches.
In the RIE method, an unnecessary product (by-product) is generally generated on sidewalls of the formed trenches. Therefore, it is more preferable to carry out a removing treatment of this unnecessary product as an after-treatment in manufacturing the semiconductor device in which the field-effect transistors having the gate insulation film are integrated. In this case, however, since the sidewalls of the formed trenches include side surfaces of the gate insulation film and so on, the prevention of an adverse effect on the gate insulation film has to be considered. Even the same operation has a relatively bigger influence on the gate insulation film as the area of the gate insulation film is smaller (in other words, as the elements are made more scaled down).